The present invention relates to a coordinate input device for use in indicating a location on a coordinate surface.
A coordinate input device of the type described, is disclosed in U.S. Pat. No. 4,717,793. The coordinate input device comprises a coordinate indicator and a coordinate input unit which defines the coordinate surface and which comprises a plurality of conductor loops under the coordinate surface. The coordinate indicator has a winding.
When the coordinate indicator is moved along the coordinate surface, the coordinate input device can successively sense a location of the coordinate indicator. This is done by magnetic coupling between the winding of the coordinate indicator and the conductor loops to make the coordinate indicator generate an electrical signal when the coordinate indicator is magnetically coupled with at least one of the conductor loops.
With this structure, the location of the coordinate indicator can be detected by monitoring the electrical signal because the electrical signal is generated from the coordinate indicator when the coordinate indicator approaches each of the conductor loops. The conventional coordinate input device is disadvantageous in that a failure of the coordinate indicator can not be distinguished from a failure in other components as long as the above-mentioned coordinate input unit is used. This is because the electrical signal disappears not only on the failure of the coordinate indicator but also on the failure of any other components. Thus, it is impossible to distinguish the failure of the coordinate indicator from the failure of other components in the coordinate input device when the coordinate input device is used.